If you are using high end East West and Kontakt samples and think the PSR-3000 sounds are anywhere near the same quality, you seriously need to have your studio monitors or your hearing checked.

Any issues you are having with dynamics has to be an error in the setting of your system as the East West Piano samples are multi layered with more velocity cross fades and dynamic range than those on your PSR-3000. There's a reason they use 20-40GB for a single sound, it's called multiple layers, multiple velocity switching, longer samples, and more samples per sound.

There isn't a "closed" keyboard made that can compete with the best VST sounds available, its just not possible with the limited RAM and CPU power that closed keyboards utilize. I don't care how well you sample 128, 256, or even 512 MB of sounds and edit them, when a single sound on a high end VST uses 10, 20, 30GB or more and has nearly every key of the instrument sample mapped, its bound to be leaps ahead of your closed system.

Computers can be problematic and I agree that using an all in one system can be much better. The key is to find an all in one system that has great sounds, tons of features, expansion capability, lots of polyphony, is intuitive, and is built very well. For me that was a Wersi Abacus. For you it seems to be a PSR-3000 which is baffling to many I am sure.